The present invention regards a cable-protective pipe section of a pipe string for a well.
The invention also regards a method of protectively arranging at least one cable on the outside of and along at least one pipe section of said pipe string. The invention is suitable for arranging the at least one cable in an essentially jointless manner along the pipe section.
The invention also regards the use of a cable protection device (cable protector) for securing the cable along said pipe section.
The well may be e.g. a petroleum well or an injection well, while the pipe string may be e.g. a completion string in the form of a production string or an injection string. In the position of use, such a string and such a cable will typically extend from the surface and down into at least one under-ground reservoir section. The invention is particularly advantageous for protecting cables in connection with open hole completions in so-called smart wells. Such smart wells may be provided with various types of equipment for monitoring, controlling and influencing well parameters and/or conditions. In other respects, use of the invention is not limited to open hole completions or smart wells, and it may equally be used in other types of wells and also cased well sections.
Upon completion of a well such as a smart well there will often be a need to pass one or more cables or cable assemblies along the well completion string. The completion string is arranged in one or more underground reservoir sections. Typically such cables are used to convey signals, power and/or fluids between the surface and equipment associated with the completion string. The signals may be control and/or measurement signals transmitted to/from various equipment in the completion string. Thus the equipment in the string may comprise, among other things, measuring instruments, sensors, actuators, valves, seals, pumps and motors. The cables can also be used to transmit driving power, e.g. electric and hydraulic power, to some of this equipment. Such cables can also be used to convey fluids such as liquids, gases, chemicals and reservoir fluids between the surface and the completion string. For the latter purpose the completion string is provided with appropriate inlet ports and/or outlet ports arranged in suitable positions along the completion string, and through which said fluids can flow when required.
As said cables are typically secured on the outside of and along the completion string, the cables will be especially vulnerable to different types of loads and associated damages that may occur both during and following the deployment of the completion string in the well. These damages may occur e.g. as a result of mechanical loads and/or erosion connected with fluid flow. This is the case especially in connection with open hole completions, where the completion string is placed in an open wellbore, and where the cables are exposed directly to an uncased formation wall, which often exhibits an uneven and rough surface, and thereby to the prevailing conditions in the wellbore. Thus there is a need to protect such external cables.
In order to avoid or reduce the loading on and damage to external cables the cables are generally arranged to be quite robust. Thus robustness can be achieved through e.g. appropriate dimensioning, choice of materials and optionally protection of the cable or cables in question. This may require a lot of well space, thus contributing to an increase in well completion costs.
The most common method of passing cables down to an open reservoir section in a well is first to install a protective and perforated well string, and optionally at least one sand screen, in the reservoir section. The completion string with cables attached, e.g. in a smart well, is the installed inside the protective pipe string, or possible inside the at least one sand screen. In this connection, different zones along the completion string are separated by means of appropriate production packers, and appropriate valves can control the fluid flow into or out of the completion string.
Norwegian patent NO 316288 describes a suitable technical solution for jointless attachment of such a cable to a pipe string by means of a split packing fixed to the outside of the pipe string.
Alternatively, and in accordance with Norwegian patent NO 314005, such cables may be passed through conduits such as protective pipes arranged between peripherally distributed and axially extending spacer strips inside a sand screen. The spacer strips are arranged between a perforated inner base pipe and an outer sand screen jacket consisting of peripheral metal wire windings.
The completion string according to the above prior art will then require the installation of two pipe strings in the open reservoir section; an outer and an inner pipe string. This completion procedure must be carried out in two independent installation operations, which is inexpedient both in terms of equipment use, expenditure of time, and costs associated with this. In terms of fluidics, this type of pipe assembly will also result in a reduced cross-section of flow for the flowing fluids. This causes an undesirable loss of fluid pressure and thereby an undesirable reduction in fluid flow rate through the completion string. Cables placed across from perforations in the protective outer pipe string will also be particularly vulnerable to erosion associated with fluid flow through said perforations.
If a pipe string fitted with a sand screen, according to NO 314005, is used in the completion of a well, the individual sand-screen-fitted base pipes must be screwed together to form a compound pipe string. Such single pipes will typically have a limited length of approximately 12 metres, and so passing a cable between said spacer strips in the sand screen of the pipe may necessitate splicing of the cable. Such a splicing operation introduces a risk of leakage in fluid bearing cables, or possibly short-circuiting of or interference in signal transmitting cables, and prolongs the installation procedure, which is undesirable both from a technical and financial point of view.